We had widespread belief in Trump-Russia collusion despite no hard evidence too. There's a word for a baseless conspiracy theory that implicates the right: "fact".
I’m not sure that you’re very well informed - your opinion is that theories of trump Russia collusion were baseless? Is that what you believe the Mueller report said?
It did say that they couldn't find hard evidence of collusion, yes.
But "baseless conspiracy theory" is practically a term of art. There was sufficient evidence of election irregularities in key battleground states to at least warrant a proper investigation. The same media companies which reported Trump-Russia collusion as hard, settled facts, however, rushed to call any suggestion of fraud a "baseless conspiracy theory" and reassured us that the 2020 elections were absolutely airtight, which -- I don't know what you have to be smoking to believe that last bit.